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| Home > Publications database > Biological and chemical induction of systemic resistance in the barley powdery mildew pathosystem |
| Dissertation / PhD Thesis/Book | PreJuSER-58897 |
2007
Forschungszentrum Jülich GmbH Zentralbibliothek, Verlag
Jülich
ISBN: 978-3-89336-475-6
Please use a persistent id in citations: http://hdl.handle.net/2128/2576
Abstract: Systemic acquired resistance (SAR) provides plants with a broad spectrum resistance to a variety of phytopathogens (fungi, bacteria and viruses). In dicotyledons the systemic resistance can be induced by both biological and chemical activators. At present it is unclear whether SAR exists in monocotyledons, however, induced resistance has been well reported. The barley-powdery mildew interaction ($\textit{Blumeria graminis f.sp. hordei, Bgh}$) was used as a test system. The effects of various biological ($\textit{Pseudomonas syringae subspecies and Xanthomonas translucens subspecies}$) and chemical (Bion$^{®}$, INA, SA and Paraquat) inducers have been analysed. Local pre-infiltration with some but not all of the bacterial strains tested led to lower systemic powdery mildew growth. The bacteria which were able to multiply quickly within barley were also able to provide protection against fungal infection. The degree of chemical resistance induced varied depending on the chemical inducer used, Bion$^{®}$ was the most effective of those tested. By using a combination of metabolite and expression analyses a hypothesis was developed concerning the mechanisms and signalling cascades involved in the development of the systemic resistance. Phenylpropanoid biosynthesis does not appear to be involved in the induced resistance observed in the course of this study. Little influence was found on the accumulation of soluble phenolic compounds following the individual local pre-treatments, whilst alterations were observed after $\textit{Bgh}$ infection. This was in agreement with the obtained expression data for PAL and CHS. In contrast three different pathogenesis-related (PR) proteins displayed differential regulation. PR-1, PR-2 and PR-3 are commonly used as markers for SAR in dicotyledons, it was shown here that Bion$^{®}$ and a $\textit{Pseudomonas syringae}$ subspecies resulted in induced PR-gene expression in barley. Paraquat led to primed expression, whilst the remaining bacteria induced local PR transcript accumulation and primed systemic expression. In some but not all systemic leaves lipoxygenase, as a marker for JA biosynthesis, was primed or induced as well as some JA dependent genes. It was hypothesised that Bion$^{®}$ mediates its systemic effects through JA signalling, whilst another signal is required for local responses possibly SA. The bacterial strains tested appear to involve a variety of signalling mechanisms which respond with differing speed and intensity. Local triggering includes reactive oxygen species (ROS) accumulation, at later time points JA and other signalling molecules induce defence responses. Paraquat pretreatment sensitised the barley plants to respond quicker and stronger to subsequent pathogen attack without having the cost of pre-emptively producing defence proteins. JA signalling is suggested to be responsible for local events whilst another signalling molecule must contribute to the systemic responses, possibly ROS. Local Paraquat pre-treatment of barley plants had a massive effect by reducing redox genes in systemic leaves as shown by differential gene expression. The results pointed out, that the systemic induced resistance in monocotyledons involves several different signalling cascades and induces various defence mechanisms. In some parameters it resembles SAR of dicotyledons but not in others. Thus the systemic induced resistance seems to be of higher complexity in monocotyledons than in dicotyledons and requires further investigation.
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